The origin of Kepler's supernova remnant

Abstract

It is now well established that Kepler's supernova remnant (SNR) is the result of a Type Ia explosion. With an age of 407yr and an angular diameter of ∼4′, Kepler is estimated to be between 3.0 and 7.0kpc distant. Unlike other Galactic Type Ia SNRs such as Tycho and SN 1006, and SNR 0509-67.5 in the Large Magellanic Cloud, Kepler shows evidence for a strong circumstellar interaction. A bowshock structure in the north is thought to originate from the motion of a mass-losing system through the interstellar medium prior to the supernova. We present results of hydrodynamical and spectral modeling aimed at constraining the circumstellar environment of the system and the amount of 56Ni produced in the explosion. Using models that contain either 0.3 M ⊙ (subenergetic) or 1.0 M ⊙ (energetic) of 56Ni, we simulate the interaction between supernova Ia ejecta and various circumstellar density models. Based on dynamical considerations alone, we find that the subenergetic models favor a distance to the SNR of <6.4kpc, while the model that produces 1 M ⊙ of 56Ni requires a distance to the SNR of >7kpc. The X-ray spectrum is consistent with an explosion that produced 1 M ⊙ of 56Ni, ruling out the subenergetic models, and suggesting that Kepler's SNR was an SN 1991T-like event. Additionally, the X-ray spectrum rules out a pure r -2 wind profile expected from isotropic mass loss up to the time of the supernova. Introducing a small cavity around the progenitor system results in modeled X-ray spectra that are consistent with the observed spectrum. If a wind-shaped circumstellar environment is necessary to explain the dynamics and X-ray emission from the shocked ejecta in Kepler's SNR, then we require that the distance to the remnant be greater than 7kpc. © © 2012. The American Astronomical Society. All rights reserved..